The process of angiography involves the visualization of the circulation system through injection of dyes. Angiography can be done on various parts of the body and can be especially important in diagnosing circulation problems in the eye, such as occlusion of the central artery. Diabetics especially suffer from vascular problems in the eye, including those with juvenile diabetes, where the disease may become aggressive, causing impaired vision. In situations involving occlusion of blood vessels in the eye, rapid diagnosis can be essential for saving the sight of the patient. Continuous oxygenated blood flow to the area is necessary to maintain physiological function of the different structures of the eye. When the blood supply is interrupted the retina is affected and sight begins to deteriorate. In many situations the lapse of time between the moment a person senses impaired sight and the moment of treatment is crucial to restore the lost vision to the previous state. Unless the occlusion is extreme, routine fundoscopy of the eye will not reveal the disease. In less severe cases the examination may show an apparently clear fundus. Angiography is necessary to assure the pathological findings of the disease in extreme cases and to ascertain the presence of disease in less severe cases.
Current equipment makes it difficult for the ophthalmologist to confirm a diagnosis of artery occlusion through imaging techniques. This is especially so in cases where the arterial circulation is only partially occluded. In cases of partial occlusion the ophthalmologist should see a delay in the infusion of the agent of contrast into the eye because of the slow passage through the narrowed or occluded blood vessel. However, current technology does not enable the ophthalmologist to simultaneously angiographically compare the problematic retina with the other healthy retina as a point of reference. The time difference necessary in examining each retina separately makes a comparison of this type impossible. In an examination of a diabetic where the disease may be affecting the eyes, information from an angiography study is already available within twenty seconds post-injection. In this early phase the agent of contrast reaches the peak degree of fluorescence due to its high concentration.
The most popular equipment in use currently is the fundus camera (such as the CF-60UVi available from Canon Inc., Lake Success, N.Y. 11042). Using the current conventional method of attempting to measure in both eyes, the procedure consists on "jumping" the camera from eye to eye while the agent of contrast circulates it is not possible to study both eyes within a twenty second period. Understandably, much vital information is lost to the ophthalmologist in the time it takes to move the camera from eye to eye and readjust it.
The procedure of retinal angiography is very dynamic and the uncaptured images are very important to the analysis of the results of the examination. Therefore, the patient is required to return for a second analysis during which the procedure is repeated. This second analysis cannot be done for at least 48 hours, until the agent of contrast has dissipated. This need for a second procedure, including a second injection, causes undue discomfort and inconvenience to the patient, while incurring a loss of a minimum of 48 hours in diagnosis time, time which may be crucial to perform the therapy which would restore the sight of the patient.
In the case of a patient suffering from Aging Macular Degeneration (AMD), this time delay causes a serious problem affecting the ability of the ophthalmologist to attempt to treat the disease. AMD is a disease which affects the macula, the part of the retina responsible for acute sight, by effecting changes in and destroying the different layers of the retina, including the photoreceptors. A certain percentage of the patients reveal a pathological growth of new vessels emerging from the choroidal vascular network. When this phenomenon occurs, a rapid decision of laser therapy intervention is required to destroy the membrane, thereby preserving the macula. Laser therapy must be performed within 72 hours of visualization of the pathological growth by retinal angiogram, so as to ensure that the disease has not progressed. Because of the inherent delay in current technology it is not possible to help a patient where the disease has attacked both eyes.
Attempts have been made using current technology to construct an apparatus capable of doing simultaneous bilateral retinal angiography, however there is as of yet no apparatus which is sufficiently simple and convenient to use so as to allow a technician to operate it. Several problems of operation are difficult to overcome with the existing technology. A simplistic approach would be to combine two standard single retinal cameras, placing one in front of each eye. The paper by De Kerk, et al. (Journal of Ophthalmology, December 1979) discloses an apparatus composed of two cameras for simultaneous bilateral angiography, requiring an operator for each of the two cameras. This is clearly a research tool and not an apparatus to be used in a doctor's office or hospital setting. First, the pupil distance does not allow the proper alignment of two single retinal cameras due to the bulk of the devices. Second, the handling by two operators causes unnecessary discomfort for the patient as both are independently attempting to align the patient's eye with the camera that they are operating. Third, the effectiveness of the procedure is low because of the complicated management necessary. Each operator uses his own judgment as to when to capture the image which may not necessarily compare with the other operator's image. Clearly the cost of two complete retinal camera systems makes analysis of this type very expensive. In addition, the De Kerk apparatus uses still camera film technology, which does not supply the necessary information on dye movement dynamics for diagnosis.
Scanning laser beam technology is the new trend in ophthalmic equipment. Use of scanning laser beam technology as disclosed in U.S. Pat. No. 4,213,678 to Pomerantzeff, U.S. Pat. No. 4,579,430 to Bille, U.S. Pat. No. 4,968,130 to Hideshima et al., and U.S. Pat. No. 5,066,116 to Sekine allows examination of the findus at a smaller pupil size and with a much lower intensity of light. However, these have only been used to observe one eye at a time.
In addition, conventional fundus cameras provide viewers through which the operator observes the eye. From this perspective it would not be possible for the operator to focus on two eyes simultaneously.
Therefore, it would be desirable to provide an apparatus for retinal imaging which would be capable of performing retinal angiography on both eyes simultaneously in an easy to operate fashion, providing significantly more accurate results of the examination without the need for a second examination, saving time and causing less discomfort to the patient, while providing a cost-effective apparatus for healthcare facilities with restricted budgets. Such an apparatus would allow acquisition of new information and thereby improve eye care.